1. Field of the Invention
The present invention relates to a drive control apparatus for an injection molding machine, which apparatus drives and controls a servomotor for moving a movable member such as a movable platen.
2. Description of the Relevant Art
Conventionally, there has been known a safety apparatus configured to stop operation of a servomotor for moving a movable member, such as a movable platen, of an injection molding machine when a safety door of the injection molding machine is opened (see, for example, Japanese Patent Application Laid-Open (kokai) No. 10 (1998)-296818).
For example, a safety apparatus of such a type operates as follows when used for a mold clamping apparatus. When a limit switch detects that a safety door is opened during movement of a movable platen toward a mold-closing direction, a detection signal that is output from the limit switch upon detection of the door being opened is fed to an over-travel terminal or zero clamp terminal of a servo circuit (servo amplifier) for driving and controlling a servomotor, to thereby quickly stop operation of the servomotor; i.e., movement of a movable platen (movable mold).
Meanwhile, the above-described conventional safety apparatus is realized by making use of a servo circuit (drive control apparatus). In many cases, a main portion of the servo circuit is realized by means of a software circuit section in order to perform various sophisticated control and processing functions at high speed and to cope with changes in specifications and upgrading. Therefore, operation of the above-described safety apparatus is also realized by a control program (software) included in the software circuit section.
Although such a software circuit section realized by means of software has the advantages as described above, the software circuit section may operate erroneously as a result of, for example, external noise. In addition, such a software circuit section may involve program bugs and may cause the CPU to fall out of control. Therefore, only a certain extent of safety and reliability of an injection molding machine has been secured.
An object of the present invention is to provide a drive control apparatus for an injection molding machine which is advantageously applied to a highly important functional section, such as a safety circuit section, of the injection molding machine in order to remarkably enhance safety and reliability of the injection molding machine, while maintaining merits attained through use of a software circuit section.
Another object of the present invention is to provide a drive control apparatus for an injection molding machine which is advantageously applied to a safety circuit section, which is a highly important functional section, in order to realize stop control of high response, as well as reliable stop control by mean of a dual system.
In order to achieve the objects as described above, the present invention provides a drive control apparatus used in an injection molding machine in order to drive and control a servomotor for moving a movable member, characterized in that among a plurality of functional sections which constitute a servo circuit connected to the servomotor, at least one functional section selected as a functional section having a higher degree of importance is constituted by a hardware circuit section realized without use of software; and the remaining functional section or sections are constituted by a software circuit section realized by making use of software.
An example of the functional section having a higher degree of importance includes a safety circuit section which detects that a safety door is opened and subsequently stops operation of the servomotor. The safety circuit section includes an open/close switch connected in series to a signal line which supplies a drive control signal to a power diver for supplying electricity to the servomotor; and a logic circuit which outputs a stop command signal upon receipt of a detection signal generated when the safety door is opened, and changes over the open/close switch by means of the stop command signal. The safety circuit section may include a delay circuit for changing over the open/close switch upon elapse of a predetermined delay time after the logic circuit has output the stop command signal.